D.C.’s decades-old loan program to assist first-time home buyers has helped thousands of families. But some buyers have taken on so much debt, they are struggling to pay bills or facing foreclosure. Nearly one in five buyers participating in the city’s program is behind on mortgage payments.

The Post examined every major project currently funded under the Housing and Urban Development program, analyzing a database of 5,100 projects worth $3.2 billion, studying more than 600 satellite images and collecting information from 165 housing agencies nationwide.